The anomeric effect Mutarotation • When compared to the β-anomer, the α-anomer is often much more stable than • Single molecule in solution can interchange expected so that in many cases [α-anomer] > [β-anomer]. between – straight chain and ring α-pyranose β-pyranose – different ring sizes – αand βanomers straight chain • Mutarotation is α-furanose β-furanose – a dynamic equilibrium – all isomers can potentially exist in solution • There is a stereoelectronic preference for conformations in which the best – energy / stability of different forms vary donor lone pair, or bond, is antiperiplanar to the best acceptor bond. 9 11 Sucrose and Lactose: Monosaccharides disaccharides • Fructose • Sucrose – Also known as cane sugar or beet sugar – Obtained commercially from sugar beet or sugar cane – Only one isomer present in solution – Easily crystallized + • Lactose – Also known as milk sugar – Primary sugar in mammalian milk (human > cow) Fischer projection Haworth projection – Also is a by-product of cheese manufacture – Not very sweet (relative intensity ≤0.3 cf sucrose) • Conversion of either anomer into the equilibrium mixture is called mutarotation – Hydrolyzed by enzyme β-galactosidase. Many adults lack this enzyme and are therefore lactose intolerant